Question about cross and dot product

[leonne]

Homework Statement

There are two points p1 pointing up p2 pointing right

Homework Equations

The Attempt at a Solution

I need to find \stackrel{\rightarrow}{p1} * r^

\stackrel{\rightarrow}{p2} X p1^

\stackrel{\rightarrow}{p2}* r^

they got \stackrel{->}{p1} * r^ =0 why is that? i know if they are perpendicual than they =0 but not sure where r^ is pointing

\stackrel{->}{p2} X p1^ =p² well i know when 2 vectors are paralle the = 0 so i am guess when they are perpendicular they are p² , but only one is a vector not sure if that matters.

\stackrel{->}{p2}* r^ = p well i am guessing from this, that r^ is parallel with p2. that's why with p1 its 0, its perpendicular, but how do we find out which way r^ is pointing?

thxs

 

[Mark44]

Homework Statement

There are two points p1 pointing up p2 pointing right

What do you mean that one "points up" and the other "points right"? A point doesn't have direction. Do you mean vectors?

Homework Equations

The Attempt at a Solution

I need to find \stackrel{\rightarrow}{p1} * r^

What is r? Is r^ supposed to be a unit vector?

\stackrel{\rightarrow}{p2} X p1^

\stackrel{\rightarrow}{p2}* r^

they got \stackrel{->}{p1} * r^ =0 why is that? i know if they are perpendicual than they =0 but not sure where r^ is pointing

If two vectors are perpendicular, their dot product is zero. The vectors themselves are not necessarily zero vectors.

\stackrel{->}{p2} X p1^ =p² well i know when 2 vectors are paralle the = 0 so i am guess when they are perpendicular they are p² , but only one is a vector not sure if that matters.

If two vectors are parallel, then one is a scalar multiple of the other. Also, their cross product is the zero vector.

\stackrel{->}{p2}* r^ = p well i am guessing from this, that r^ is parallel with p2. that's why with p1 its 0, its perpendicular, but how do we find out which way r^ is pointing?

Not much of what you wrote makes sense. Please include all of the given information for this problem.